Olefins are traditionally produced from petroleum feedstock by catalytic or steam cracking processes. These cracking processes, especially steam cracking, produce light olefin(s) such as ethylene and/or propylene from a variety of hydrocarbon feedstock. Ethylene and propylene are important commodity petrochemicals useful in a variety of processes for making plastics and other chemical compounds.
The petrochemical industry has known for some time that oxygenates, especially alcohols, are convertible into light olefin(s). There are numerous technologies available for producing oxygenates including fermentation or reaction of synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials including coal, recycled plastics, municipal waste or any other organic material. Generally, the production of synthesis gas involves a combustion reaction of natural gas, mostly methane, and an oxygen source into hydrogen, carbon monoxide and/or carbon dioxide. Syngas production processes are well known, and include conventional steam reforming, autothermal reforming, or a combination thereof.
Methanol, the preferred alcohol for light olefin production, is typically synthesized from the catalytic reaction of hydrogen, carbon monoxide and/or carbon dioxide in a methanol reactor in the presence of a heterogeneous catalyst. For example, in one synthesis process methanol is produced using a copper/zinc oxide catalyst in a water-cooled tubular methanol reactor. The preferred methanol conversion process is generally referred to as a methanol-to-olefin(s) process, where methanol is converted to primarily ethylene and/or propylene in the presence of a molecular sieve.
Molecular sieves are porous solids having pores of different sizes such as zeolites or zeolite-type molecular sieves, carbons and oxides. The most commercially useful molecular sieves for the petroleum and petrochemical industries are known as zeolites, for example aluminosilicate molecular sieves. Zeolites in general have a one-, two- or three-dimensional crystalline pore structure having uniformly sized pores of molecular dimensions that selectively adsorb molecules that can enter the pores, and exclude those molecules that are too large.
There are many different types of molecular sieves well known to convert a feedstock, especially an oxygenate containing feedstock, into one or more olefin(s). For example, U.S. Pat. No. 5,367,100 describes the use of a well known zeolite, ZSM-5, to convert methanol into olefin(s); U.S. Pat. No. 4,062,905 discusses the conversion of methanol and other oxygenates to ethylene and propylene using crystalline aluminosilicate zeolites, for example Zeolite T, ZK5, erionite and chabazite; U.S. Pat. No. 4,079,095 describes the use of ZSM-34 to convert methanol to hydrocarbon products such as ethylene and propylene; and U.S. Pat. No. 4,310,440 describes producing light olefin(s) from an alcohol using a crystalline aluminophosphates, often represented by ALPO4.
One of the most useful molecular sieves for converting methanol to olefin(s) is a silicoaluminophosphate molecular sieves. Silicoaluminophosphate (SAPO) molecular sieves contain a three-dimensional microporous crystalline framework structure of [SiO2], [AlO2] and [PO2] corner sharing tetrahedral units. SAPO synthesis is described in U.S. Pat. No. 4,440,871, which is herein fully incorporated by reference. SAPO is generally synthesized by the hydrothermal crystallization of a reaction mixture of silicon-, aluminum- and phosphorus-sources and at least one templating agent. Synthesis of a SAPO molecular sieve, its formulation into a SAPO catalyst, and its use in converting a hydrocarbon feedstock into olefin(s), particularly where the feedstock is methanol, is shown in U.S. Pat. Nos. 4,499,327, 4,677,242, 4,677,243, 4,873,390, 5,095,163, 5,714,662 and 6,166,282, all of which are herein fully incorporated by reference.
Typically, molecular sieves are formed into molecular sieve catalyst compositions to improve their durability in commercial conversion processes. The collisions within a commercial process between catalyst composition particles themselves, the reactor walls, and other reactor systems cause the particles to breakdown into smaller particles called fines. The physical breakdown of the molecular sieve catalyst composition particles is known as attrition. Fines often exit the reactor in the effluent stream resulting in problems in recovery systems. Catalyst compositions having a higher resistance to attrition generate fewer fines, less catalyst composition is required for conversion, and longer life times result in lower operating costs.
Molecular sieve catalyst compositions are formed by combining a molecular sieve and a matrix material usually in the presence of a binder. The purpose of the binder is hold the matrix material, often a clay, to the molecular sieve. The use of binders and matrix materials in the formation of molecular sieve catalyst compositions is well known for a variety of commercial processes. It is also known that the way in which the molecular sieve catalyst composition is made or formulated affects catalyst composition attrition.
Example of methods of making catalyst compositions include: U.S. Pat. No. 5,126,298 discusses a method for making a cracking catalyst having high attrition resistance by combining two different clay particles in separate slurries with a zeolite slurry and a source of phosphorous, and spray drying a mixture of the slurries having a pH below 3; U.S. Pat. No. 4,987,110 and 5,298,153 relates to a catalytic cracking process using a spray dried attrition resistant catalyst containing greater than 25 weight percent molecular sieve dispersed in a clay matrix with a synthetic silica-alumina component; U.S. Pat. Nos. 5,194,412 and 5,286,369 discloses forming a catalytic cracking catalyst of a molecular sieve and a crystalline aluminum phosphate binder having a surface area less than 20 m2/g and a total pore volume less than 0.1 cc/g; U.S. Pat. No. 4,542,118 relates to forming a particulate inorganic oxide composite of a zeolite and aluminum chlorhydrol that is reacted with ammonia to form a cohesive binder; U.S. Pat. No. 6,153,552 claims a method of making a catalyst, by drying a slurry of a SAPO molecular sieve, an inorganic oxide sol, and an external phosphorous source; U.S. Pat. No. 5,110,776 illustrates the formation of a zeolite containing catalytic catalyst by modifying the zeolite with a phosphate containing solution; U.S. Pat. No. 5,348,643 relates to spray drying a zeolite slurry with a clay and source of phosphorous at a pH of below 3; U.S. patent Ser. No. 4,973,792 is directed to a conversion process using a formulated molecular sieve catalyst composition, however, there is no mention of the solid content of the slurry spray dried, nor any discussion of the amount of liquid medium in the SAPO-34 added to the slurry; U.S. patent application Ser. No. 09/891,674 filed Jun. 25, 2001 discusses a method for steaming a molecular sieve to remove halogen; U.S. Pat. No. 5,248,647 illustrates spray drying a SAPO-34 molecular sieve admixed with kaolin and a silica sol; U.S. Pat. No. 5,346,875 discloses a method for making a catalytic cracking catalyst by matching the isoelectric point of each component of the framework structure to the pH of the inorganic oxide sol; Mäurer, et al, Aggregation and Peptization Behavior of Zeolite Crystals in Sols and Suspensions, Ind. Eng. Chem. Vol. 40, pages 2573–2579, 2001 discusses zeolite aggregation at or near the isoelectric point; PCT Publication WO 99/21651 describes making a catalyst by drying a mixture of an alumina sol and a SAPO molecular sieve; PCT Publication WO 02/05950 describes making a catalyst composition of a molecular sieve containing attrition particles with fresh molecular sieve; and WO 02/05952 discloses a crystalline metallo-aluminophosphate molecular sieve and a matrix material of an inorganic oxide binder and filler where the molecular sieve is present in an amount less than 40 weight percent relative to the catalyst weight and a preferable weight ratio of the binder to molecular sieve close to 1.
Although these molecular sieve catalyst compositions described above are useful in hydrocarbon conversion processes, it would be desirable to have an improved molecular sieve catalyst composition having better attrition resistance and commercially desirable operability and cost advantages.